1. Field of the Invention
The invention relates to an optical printer, comprising an information-controlled light source, a mirror system which comprises a rotatable mirror and a circular-to-linear convertor which consists of optical fibers, the ends of said optical fibers being arranged in a circle which is concentric with the axis of rotation of the rotatable mirror at the entrance of said convertor while the ends of the optical fibers are arranged in a straight line opposite a photosensitive record carrier at the exit of said convertor.
2. Description of the Prior Art
From U.S. Pat. No. 3,770,910 a device is known for the recording of information which consists of a light source, a rotatable mirror and a circular-to-linear convertor which consists of optical fibers. Therein, the ends of the optical fibers which are arranged in a circular at the entrance of the convertor extend parallel to the axis of rotation of the rotatable mirror, their end faces being bevelled so that they enclose an angle of approximately 45.degree. with respect to the light beam reflected by the rotatable mirror. Consequently, only a part of the light is coupled into the optical fibers.
It is the object of the invention to improve the optical coupling between the light source and the circular-to-linear convertor by reducing the loss of light. The loss of light is caused by reflection from the end faces of the optical fibers and by the re-emergence of light from the optical fibers because a part of the light coupled-in arrives on the coating of the optical fibers in an unfavorable direction.
To this end, the printer in accordance with the invention is characterized in that the mirror system comprises a further, conical mirror which opens towards the circular-to-linear convertor and whose symmetry axis coincides with a light beam from the light source and with the axis of rotation of the rotatable mirror, said conical mirror being arranged so that the light beam which is emitted by the light source and which is reflected by the rotatable mirror is axially coupled into each time one or more of the circularly arranged ends of the optical fibers at the entrance of the circular-to-linear convertor. It is an important improvement that by multiple deflection the light beam is coupled into the circular-to-linear convertor parallel to the circularly arranged ends of the optical fibers.
A preferred embodiment of the device in accordance with the invention is characterized in that the rotatable mirror is constructed by grinding the end face of a rotor shaft of an electric motor so as to have a plane surface finish. Such a mirror can be simply and inexpensively manufactured and avoids an increased moment of inertia of the rotor shaft, so that short starting times are ensured when the optical printer is switched on.
A further preferred embodiment of the device in accordance with the invention comprises a sensor for the position of the rotatable mirror, said sensor being electrically connected to the control circuit for the light source and to a drive for the record carrier. The sensor supplies the control circuit for the light source and the drive for the record carrier with the necessary pulses for correct operation of the optical printed, i.e. synchronized movement of the rotatable mirror and the record carrier.
A further embodiment of the device in accordance with the invention is characterized in that the light source is formed by a laser. The light beam is thus concentrated and the lens systems otherwise required for concentrating the light beam may be omitted.
Some embodiments of a printer in accordance with the invention will be described in detail hereinafter with reference to the drawings.